Phosphorus furnace operation



Filed July 11. 1931 l l I Patented Mar. 29, 1934 sin?.

PHSPHORUS FURNACE OPERATION Rothe Weigel, Nashville, Tenn., assignor to Victor Chemical Works, a corporation of Illinois Application July 11, 1931, Serial No. 550,120

6 Claims.

The present invention relates to improvements in the production of phosphorus, more particularly in volatilization furnaces of the type of blast furnaces. It willl be fully understood from the following description, illustrated by the accompanying drawing, in which a furnace suitable for carrying the invention into effect is illustrated in section.

In the blast furnace production of phosphorus,

l@ various dimculties have hitherto been encountered which have seriously affected the operation. Among these difficulties are the production of considerable quantities of very fine dust or fume which are carried by the gases, are difficult to i5 remove and which, in the further handling of the gases, contaminate the phosphorus, produce slaggy masses in the chambers for combustion of the phosphorus-containing gases, and contaminate and reduce the yield of phosphate prod- 2@ ucts formed. Furthermore, in the furnace operation, difliculty has been encountered in securing adequate furnace temperatures for the most complete volatilization of the phosphorus possible, and for reducing the viscosity of the slag and the phosphate content of the latter. By

operating in accordance with the present invention, the proportions of fume, dust and other impurities carried in the gases from the furnace are materially reduced, higher temperatures are se- 39 cLued in the hearth, with more effective volatilization of phosphorus, the phosphate content of the slag is reduced, and in general, the yield of phosphorus from the furnace is materially improved, as well as the purity of the phosphorus or phosphate products formed from it.

In the normal operation o-f blast furnaces for the production of phosphorus, as well as for the production of iron, it has hitherto been customary to control the operation of the furnace so as to 40 secure as nearly as possible a uniform descent of the charge through the furnace, and to avoid as far as possible the irregularities in operation and control resulting from temporary partial or complete cessation of movement of the stock through the furnace, known as hanging, followed by sudden movements of the entire mass of stock in the column. In this normal method of operation, the downward movement of the stock through the furnace is opposed and the stock partially supported by the pressure of the airblast. I have found that in operating a phosphorus blast furnace in the usual and customary manner, the various defects in operation hereinbefore referred to arise. I have furthermore (Cl. Zit-223) of operation of the furnace, mainly in directions hitherto regarded as highly undesirable, a greatly improved yield of phosphorus can be secured, with a reduction in phosphate content of the slag, and likewise a material reduction in dust, fume and other undesirable matter carried by the phosphorus-bearing gases from the furnace. In carrying out the present invention, the operation is so conducted as to avoid a uniform descent of the charge through the stack of the fur- 05 nace and to cause its descent to take place intermittently at regular or irregular intervals; and by the drop or descent of the stock at such intervals, to secure a substantial compacting of the material in the furnace. The increased compactness of the stock column in the furnace is shown by a substantial increase in the blast pressure when operating in accordance with the present invention over the blast pressure required in operation in the same furnace with the customary continuous, uniform descent of stock. I have found that a convenient way of securing such a controlled descent of the stock at intervals and compacting of the stock column is by a partial or complete stoppage of the blast, although, as is readily apparent, `other means may be employed for securing this result.

Thus, I have found that the increased compactness of the stock column secured in accordance with the present invention may be aided by using the constituents of the charge in smaller particle sizes than has hitherto been customary. Thus, in blast furnace operation, it is `customary to employ for fuel a furnace coke of an average size of one and three-eighths inch by three and a quarter inch. In operating in accordance with the present invention it is preferred to employ for part or all of the fuel coke a smaller size, for example, about one inch by one and three-eighths inch. Furthermore, the construction of the furnace itself may desirably be modified when operating in accordance with the present invention, for example, by reducing the batter of the stack o1` by providing in the lower portion of the stack, above the bosh, a section substantially cylindrical T in form, having no batter or a substantially negligible batter. The accompanying drawing illustrates a furnace of this character in which the invention may suitably be carried out.

Batter is the slope of the furnace walls as 1U measured by the number of inches the radius of the furnace changes per foot of change in height. An inward batter is one where there is a decrease in radius toward the top of the furnace. 119

Referring more particularly to the drawing, the numeral 5 indicates the hearth of the furnace and the numeral 6 the bosh, above which is the stack 7. In the furnace illustrated, the lower portion of the stack, designated as 8, has substantially vertical walls with no appreciable inward batter, this section of the stack varying from ten to twenty feet in height. Above it, the upper portion of the stack, designated Se, has an inward batter ranging from 0.375 to 0.575. It is preferred to operate with as low a batter as possible. The height of the stack may vary Widely, say from 40 to 100 feet, and the height of the section 8 may suitably be from 10 to 25 feet, preferably about 15 feet. Above lthe stack, the furnace is provided with a cap 9 having a gas outlet 10, through which the furnace gases containing volatilized phosphorus pass to suitable dust and nlm collectors (not shown). ri'he cap 9 is likewise provided with a suitable form of feed device, for example, a double bell feed hopper 11.

The blast furnace is started with coke and slag in the usual manner, and is then supplied with phosphate mineral, silicious material and carbon for reduction of the phosphate, and with coke for fuel in the requisite quantities. The phosphate mineral may suitably be run-of-mine phosphate rock, ground and briquetted in small briquettes, say 1.5 to 2 inches square in cross section or thereabouts with silicious material and carbonaceous material, the silicious material and carbonaceous material being present in proportions equal to or less than those required for re- ,June 8, 1931.

. operation. The fuel carbon is supplied preferably as coke and in operating in accordance with the present invention, the size of coke employed is preferably smaller than ordinary furnace coke, as` hereinbefore pointed out. The proportion of fuel coke to briquettes and silica is adjusted to secure the desired hearth temperatures and in ordinary practice will range from 67% to 72% of the briquettes and silica. The burden and fuel are fed in suitable quantities, as in ordinary practice, the unit charges of fuel coke varying from 7500 to 12000 lbs. and those of the burden being adjusted accordingly. l

In operating the furnace in accordance with the present invention, at intervals which may be irregular or regular, but are preferably regular, the blast is slacked or reduced either partly or completely, preferably by diverting it from the the furnace. rIhe slacking or checking of the blast is effected before any substantial normal descending movement of the charge in the furnace has taken place. As a result of slacking the blast, the lifting force of the blast being removed from the stock, it drops rapidly and in its fall the column of stock is greatly compacted. As hereinbefore pointed out, this compacting of the stock is clearly indicated by the greater blast pressures required for operation in accordance with the present invention. For example, in the same furnace, operating in accordance with the usual methods with substantially uniform descent of the stock through the furnace, the average blast pressure was in the order of 12 to 13.5 lbs. Operating in accordance with the present invention, the blast pressure required in the same furnace is in excess of 14 lbs., and in general from 14.5 te 15 lbs. Higher hearth temperatures, in general above 1600 C. are secured, as indicated by greater fluidity and lower phosphate content of the slag, and by increased volatlization of phosphorus.

In plant operation, it is preferred that the blast be slacked or checked and the stock column compacted at regular intervals, say once an hour. By so doing with a furnace such as that above described, substantially the entire movement of the stock through the furnace takes place upon reduction of the blast, the stock column being practically stationary during the period the blast is on. Slag is preferably tapped from the hearth just before or only a short time before the blast is checked, so that too great a body of slag will not be present in the hearth during the rapid drop of the stock column.

By operating in accordance with the present invention, the proportions of dust and fume in the furnace gases are materially reduced with relation to the proportions of phosphate mineral charged. Thus, in normal operation as hitherto conducted, with continuous descent of the stock, in general from about 0.12 to 0.20 lbs. of dust and fume are collected for each pound of phosphorus pentoxide charged. When operating in accordance with the present invention, with a compacted column of stock, the proportion of dust and fume collected is reduced to 0.095 lbs. per pound of phosphorus pentoXide charged and in general is around 0.085 or less. Furthermore, the proportion of dust and fume which is of an extremely fine character, not collectible in ordinary separating devices, is markedly reduced, at least from one-third to one-half, and the effect of this material on the purity of phosphorus or phosphoric acid produced is hence greatly decreased. The proportion of phosphate contained in the slag is likewise materially reduced. The overall phosphorus yield is increased and improved volatilization of phosphorus is secured.

I claim:

1. In the production of phosphorus by Volatilization in a blast furnace from a stock containing phosphate mineral and fuel constituents with combustion of the latter, the method which comprises maintaining the stock in the furnace in a compacted state substantially throughout the operation of the furnace, said compactness being such as to require an increase in blast pressure of the order of 10% and upwards over the pressure normally required for a stock consisting essentially of coke having an average size of 1% by 31/4," and briquettes of phosphatic material 11/2 to 2 square in cross-section, said briquettes comprising about X3 ofthe charge. Y

2. In the production of phosphorus by volatili.- Zation in a blast furnace from a stock containing phosphate mineral and fuel constituents with combustion of the latter, the method which com-- prises effecting rapid downward movement of the stock column in the furnace at frequent intervals throughout the operation of the furnace, thereby compacting the stock column.

3. In the production of phosphorus by volatilization in a blast furnace from a stock containing phosphate mineral and fuel constituents with combustion of the fuel constituents, the method which comprises maintaining the stock in the furnace substantially stationary during combustion of the fuel constituents thereof, and at fre 150 quent intervals throughout the operation of the furnace effecting rapid downward movement of the stock, thereby compacting the stock column.

4. In the production of phosphorus by volatilization in a blast furnace from a stock containing phosphate mineral and fuel constituents with combustion of the fuel constituents by applied blast, the method which comprises intermittently checking the blast, thereby effecting rapid down- Ward movement of the stock column.

5. In the production of phosphorus by volatilization in a blast furnace by stock containing phosphate mineral and fuel constituents with combustion of the latter by applied blast, the method which comprises maintaining the stock in the furnace substantially stationary while applying the blast, thereby effecting combustion of the fuel constituents, and intermittently checking the blast, thereby effecting rapid downward movement of the stock column.

6. In the production of phosphorus by volatilization in a blast furnace from a stock containing phosphate mineral and fuel constituents with combustion of the latter by applied blast, the method which comprises maintaining the stock in the furnace substantially stationary -for periods while continuing the blast, thereby effecting combustion of the fuel constituents, intermittently checking the blast, thereby effecting rapid downward movement of the stock column, and adjusting the periods at which the blast is checked to cause substantially the entire movement of the stock to take place during the periods of checking the blast.

ROTHE WEIGEL. 

